Process for producing solid polyurethane curing agents
The present invention relates to a process for producing a solid, internally and externally blocked polyurethane curing agent based on a (cyclo)aliphatic polyisocyanate, in which, in the sequence of steps a) to d), a) i) at least one internally blocked (cyclo)aliphatic polyisocyanate and ii) at least one lactam and/or at least one aliphatic alcohol are dissolved in a solvent to produce a reaction mixture, b) the reaction mixture is heated and reacted, c) the reacted reaction mixture is cooled until product precipitates, and d) liquid solvent and any unreacted dissolved reactants and precipitated product are mechanically separated from one another.
1. A process for producing a solid, internally and externally blocked polyurethane curing agent based on a (cyclo)aliphatic polyisocyanate, in which, in the sequence of steps a) to d),
a) i) at least one internally blocked (cyclo)aliphatic polyisocyanate,
wherein the internally blocked (cyclo)aliphatic polyisocyanate is an internally blocked cycloaliphatic polyisocyanate formed from only polyisocyanates having at least one cyclically and at least one acyclically aliphatically bonded isocyanate group, and
ii) at least one lactam and/or at least one aliphatic alcohol are dissolved in a solvent to produce a reaction mixture,
wherein the solvent is an ether selected from a group consisting of a diisopropyl ether and a methyl tert butyl ether,
b) the reaction mixture is heated and reacted,
c) the reacted reaction mixture is cooled until product precipitates, and
d) liquid solvent and any unreacted dissolved reactants and precipitated product are mechanically separated from one another.
2. The process according to claim 1 , wherein the internally blocked (cyclo)aliphatic polyisocyanate is a uretdione or isocyanurate.
3. The process according to claim 1 , wherein the polyisocyanate used is an internally blocked polyisocyanate of isophorone diisocyanate.
4. The process according to claim 1 , wherein the reactants are
i) an isocyanurate group-containing polyisocyanate and a lactam or
ii) a uretdione group-containing polyisocyanate and an alcohol.
5. The process according to claim 1 , wherein the lactam and/or the alcohol is selected from the group consisting of ε-caprolactam, ethylene glycol, propane-1,2-diol, butylene glycol, pentanediol, hexanediol, heptanediol, octanediol, nonanediol, decanediol, undecanediol, dodecanediol, trimethylolpropane, and the OH-terminated oligoesters of the aforementioned diols with dicarboxylic acids having 4 to 12 carbon atoms.
6. The process according to claim 1 , wherein in step b) after the heating the reaction mixture has a temperature of 35 to 90° C.
7. The process according to claim 1 , wherein the reaction in step b) is effected over a period of one hour to two days.
8. The process according to claim 1 , wherein in step d) liquid solvent and any unreacted dissolved reactants and precipitated product are separated from one another by means of decantation, filtration or centrifugation.
9. The process according to claim 1 , wherein the process further comprises:
e) the precipitated product is freed of adhering solvent and/or
f) the liquid solvent and any unreacted dissolved reactants are recycled.